The present invention relates to a method and apparatus for coating and/or encapsulating a six-sided fibrous object or batting with thermoplastic material.
Insulating materials are frequently manufactured in the form of six-sided objects, referred to herein as batting, from fibrous materials such as rock fibers, glass fibers, slag fibers, wool fibers, and the like. These materials are used as thermal and acoustic insulators in a variety of applications. One problem associated with the fibrous batting is that its fibrous nature causes surface fibers to break away from the batting, particularly on handling. This not only can reduce the effectiveness of the insulator, but can also contaminate the atmosphere with fibers. In order to prevent this, it has been a common practice to coat the batting with a thermoplastic material. Preformed nonwoven web material composed of polymer fibers has been adhered to the surface of fibrous batting. These preformed layers become an integral part of the batting. This approach for coating the batting has not been entirely satisfactory because the adhesive used for securing the preformed layers to the batting may result in a fire hazard and also may detract from the insulation properties of the final product. Moreover, it is difficult to obtain a complete encapsulation of the batting.
PCT Application No. PCT/DK93/00064 discloses a method of applying a polymer coating onto a batting surface. The apparatus disclosed in the PCT application includes (a) a meltblowing die wherein micro-sized thermoplastic fibers are applied to a fibrous surface by the meltblowing process, and (b) melt spray nozzles wherein a gas/polymer mixture is applied to the fibrous surface.
With the melt spray apparatus, a number of nozzles arranged in a line across the surface to be coated discharge the gas/polymer stream onto the batting surface. A number of such nozzles, or pressure guns, can also be positioned circumferentially around the batting to coat four sides of the batting.
While the PCT application discloses coating four sides using the melt spray apparatus, it discloses only the coating of the upper and lower sides using the meltblowing apparatus. In the meltblowing apparatus, a suction device in accordance with the teachings of the PCT application is required to be positioned on the opposite side of the surface being coated. Because the batting generally is much wider than thick, the suction device could not be used in coating the sides of a thick batting.
Meltblowing offers the advantage over melt-spraying of producing a more uniform coating, but as demonstrated in the PCT Application, has not been successfully used to coat a six-sided batting by prior techniques.
Meltblowing is a term used in the nonwovens industry to describe a process wherein a series of thermoplastic filaments (or fibers) are extruded from a die while converging sheets of hot air contact opposite sides of the filaments imparting drag forces thereto. The drag forces draw down or stretch the filaments to microsize diameters and deposit them on a surface as randomly entangled fibers forming a nonwoven web. Nonwoven webs have been used as fibers, absorbents, and coatings to name a few.